A book written by a Kabbalist is part of the spiritual world. This is so even if the author lowers the power and style of the writing by many degrees in an effort to clarify the subject for the reader. It is like Zivug Arkanat Rosh, where the Upper Level comes down to the lower level, like a mother bending over her baby.
Therefore, despite the reduced level of its delivery, the work itself is perfect and spiritual, and we must accept its higher truth. We cannot agree with one aspect of it while rejecting another. If we do, this is only an indication of our own imperfection, our lack of qualities necessary to accept and properly assess this information.